Coordinate haproxy and keepalived restarts

Keepalived and haproxy cooperate to provide control plane HA in
kolla-ansible deployments.
Certain care should be exerted to avoid prolonged availability
loss during reconfigurations and upgrades.
This patch aims to provide this care.
There is nothing special about keepalived upgrade compared to
reconfig, hence it is simplified to run the same code as for
deploy.
The broken logic of safe upgrade is replaced by common handler
code which's goal is to ensure we down current master only after
we have backups ready.

This change introduces a switch to kolla_docker module that allows
to ignore missing containers (as they are logically stopped).
ignore_missing is the switch's name.
All tests are included.

Change-Id: I22ddec5f7ee4a7d3d502649a158a7e005fe29c48